1. Field of the Invention
This invention relates to an internal combustion engine, and more particularly, to an internal combustion engine having a stationary portion and a rotary portion, in which rotational power is supplied to the rotary portion from the controlled internal combustion of a fuel.
2. Background Information
The basic functions of an internal combustion engine are the intake of a combustible mixture into a working area, the compression of the mixture, the ignition of the mixture with its subsequent expansion, and the removal of combustion by products to an exhaust system. The expansion portion of the cycle is the part which produces useful work. Traditional reciprocating internal combustion engines use the reciprocating motion of a piston in a cylinder to perform these functions. Motion is then obtained by connecting the piston with a connecting rod to an eccentric portion of a crankshaft.
In a four stroke cycle engine, valves in the top of the cylinder are used to control the intake of the mixture and the release of exhaust gasses. In the first inward stroke, away from the cylinder head, the exhaust valve is shut and the intake valve is opened, so that the piston motion draws the mixture inward. In the first outward stroke, the intake valve is closed and the motion of the piston is used to compress the mixture. In the second inward stoke, the mixture is ignited and allowed to expand. In the second outward stroke, the exhaust valve is opened, and the motion of the piston is used to expel exhaust gasses. A particular disadvantage of this type of engine is that two revolutions of the crankshaft are required for a single power producing expansion cycle.
In a two stroke cycle engine, the valves are eliminated, and intake and exhaust ports are located on opposite sides of the cylinder just above the farthest inward point of piston travel. After each inward (expansion) stroke, exhaust gases under pressure leave the cylinder through the exhaust port, and a new explosive mixture is swept in through the intake port, sweeping most of the remaining gasses out in a process called scavenging. A particular advantage of this type of engine is the fact that one expansion cycle occurs per revolution of the crankshaft. Disadvantages are the inefficiency of the scavenging process, which leaves some exhaust gasses in the cylinder to interfere with efficient combustion, and the fact that external means are often required to blow the combustible mixture into the cylinder.
The diesel engine is another type of internal combustion engine, which is commonly built in both two stroke cycle and four stroke cycle versions reciprocating devices. A Diesel engine typically receives air, instead of a mixture of vaporized fuel and air, at the beginning of each compression stroke. The air is then compressed by the piston motion much harder than the mixture of fuel and air in a gasoline type engine, until a temperature of about 900 to 1100 degrees Fahrenheit is reached with a pressure somewhat above 450 pounds per square inch. Near the end of the compression stroke, Diesel fuel is injected into the cylinder by means of a fuel injector, which can perform this operation working against such pressures. The temperature of the air within the cylinder is high enough to begin the combustion process, so a spark plug is not used.
Rotary internal combustion engines are constructed so that a tangential force is applied to a spinning rotor by gasses expanding after combustion, instead of using the inward motion of a piston driven by such gasses. To make this work, the gasses are allowed to expand between stationary surfaces and a surface extending radially from the rotor to be pushed thereby.
3. Description of the Prior Art
An early example of a rotary internal combustion engine is found in U.S. Pat. No. 688,335, issued to J.H. Reed on Dec. 10, 1901, which describes an engine having a rotor in which a piston is slid inward and outward at an angle under the control of a stationary cam. An arcuate combustion chamber with an open end is mounted on an angularly oscillating sector which is pivotably mounted coaxial with the rotor. Means, including an external compressor, are provided to supply an explosive gas to the combustion chamber. The gas within the chamber is exploded using an electrode, and the tangential forces acting on the side of the piston, since it forms the end of the chamber, propel the rotor as the oscillating sector is returned to its original position. The Reed engine does not provide for expansion of combustion gasses in an enlarging combustion chamber. The sliding piston is simply impacted by an impulse from the exploding gas to operate somewhat like an undershot waterwheel.
One way of allowing combustion gasses to propel a rotor while expanding is to provide a rotor spinning within a generally cylindrical housing, where the rotor includes an abutment extending outward to the internal surface of the housing, and where the housing includes an abutment sliding outward to permit the adjacent passage of the rotor abutment and inward after such passage. The expansion of gasses is allowed to occur between these abutments, thereby propelling the rotor. An example of this type of engine is found in U.S. Pat. No. 1,239,853, which was issued to F. Walter on Sep. 11, 1917. This patent shows an engine having a combustion chamber, including a spark plug, built into the rotor abutment. This combustion chamber has an outlet in a trailing wall, which is normally shut by a valve. An explosive mixture, pre-compressed by an external piston, is fed into the combustion chamber through a hole in the shaft of the rotor, to be exploded after opening of the valve, and after the sliding abutment moves inward following the rotor abutment. Expanding gasses then propel the rotor, pushing against the sliding abutment.
A second example of a rotary engine is described in U.S. Pat. No. 1,970,003, which was issued to H.M. Fenati on Aug. 14, 1934. The Fenati patent describes a rotor, with a semicircular groove around most of its outer surface, operating in a housing having a semicircular groove around most of its inner surface, together forming an annular chamber with a circular cross-section. An abutment surface extends outward as a part of the rotor to operate in the annular chamber. A sliding abutment in the housing is moved outward to clear the rotor abutment surface, and is moved inward after its passage. A combustion chamber with a spark plug, supplied by an externally pre-compressed explosive mixture, is provided in the housing outside the sliding abutment. When the abutment, which also acts as a valve, is moved inward, burning and expanding gasses are admitted by the valve to propel the rotor by expanding between the sliding abutment and the rotor abutment.
Another way to provide a rotary engine is to provide a rotor spinning within a housing having an outwardly extended porti between a combustion region and an exhaust port, along with a rotor vane which is moved outward into the extended portion. Examples of rotary engines built in this way have been described, in U.S. Pat. No. 897,260, which was issued to C.H. Luther, Jr. on Aug. 25, 1908, in U.S. Pat. No. 2,018,306, which was issued to D.F. Hunt on Oct. 22, 1938 and in U.S. Pat. No. 2,146,877, which was issued to C. Appleton on Feb. 14, 1939. These engines have rotors carrying radially slidable pistons moved inward and outward by stationary cams. Each engine housing includes an intake port, a combustion chamber with a spark plug, an exhaust port. Each rotor has means, travelling ahead of each piston as the rotor turns, for transversely sealing the outward extended section of the housing. In the C.H. Luther, Jr. invention, a radially sliding vane moved by a second stationary cam track is used for this purpose; in the D.F. Hunt and C. Appleton inventions, a sealing bar or vane is held against the surface of the outwardly extended section.
In the prior art rotary engines, described above, as each piston passes the intake port, it is drawn inward, creating a suction to pull a mixture of air and fuel inward. As each vane enters region of the combustion chamber, it is moved outward to bisect the outwardly extended portion of the housing. As each piston enters the region of the combustion chamber, it is moved outward to compress the mixture of air and fuel, which is then exploded by means of the sparkplug. The expanding gasses from the explosion produce a pressure on the portion of the vane extending into the outwardly extended portion of the housing, thereby propelling the rotor. As the vane passes the exhaust port, it is pulled inward and the gasses within the outwardly extended portion of the housing are vented through the port. While the engines described in the C.H. Luther, Jr. and D.F. Hunt patents each have three pistons and a single combustion chamber, the engine described in the C. Appleton patent has two pistons and two combustion chambers.
U.S. Pat. No. 4,617,886, issued to S.R. Mach on Oct. 21, 1986, shows four pistons mounted to slide radially in a rotor. Reciprocating motion of the pistons is brought about by means of connecting rods extending between each piston and a shaft displaced from the center of rotation of the rotor. Two chambers are formed in each piston, separated by vanes in the rotor, over which the pistons slide. As these chambers pass intake slots, one is filled with fuel while the other is filled with air. The outer housing includes a section, which surrounds the intake portion of the engine, fitting tightly around the rotor. The remaining section is an arc coaxial with the center of the shaft, having a smaller diameter than the outside of the rotor, but extending outward therefrom because of the displacement between the two centers. This section forms a combustion chamber, having a spark plug and one end and an exhaust port at the opposite end.
Another way to build a rotary internal combustion engine, which has met with commercial success, is to mount a rotor so that it turns at a first rotational speed about an eccentric portion of a shaft turning at a second rotational speed. This method is described in U.S. Pat. No. 2,880,045, issued to F. Wankel on Mar. 31, 1959, in U.S. Pat. No. 2,988,008, issued to F. Wankel on Jun. 13, 1961, and in U.S. Pat. No. 2,947,290, issued to W.G. Froede on Aug. 2, 1960. The two rotational motions are tied together, for example, by a gear with internal teeth on the rotor meshing with a gear with external teeth on the shaft. The rotor has several (typically three) equally spaced, outward extending apex portions where seals are placed to operate on an internal surface of a stationary housing. For the seals to operate properly, the internal surface must have the shape which is generated by the kind of apex motion. Thus, it must have an epitrochoidal shape, typically with two lobes. During rotation, the space between the rotor and the inner surface of the housing is formed into several working chambers compressing trapped gasses and allowing their expansion as required in the operation of a four stroke cycle engine. Primary advantages of the Wankel type of engine are its simplicity, compared to conventional reciprocating engines, and its lack of reciprocating parts, which allows its operation at high rotational speeds. A primary disadvantage of the Wankel type of engine is the difficulty of producing the complex shapes of the rotor and the inner housing surface. A method for machining such surfaces is disclosed in U.S. Pat. No. 2,870,578, issued to O. Baier on Jan. 27, 1959.
Air compressors and various types of pumps use many of the mechanisms also used in internal combustion engines. For example, reciprocating compressors use pistons driven by crankshafts and valve mechanisms. U.S. Pat. Nos. 2,880,045 and 2,988,008 to Wankel, describe the application of rotary piston machines in pumps or compressors as well as in internal combustion engines. U.S. Pat. No. 3,269,371, issued to K. Eickmann on Aug. 30, 1969, describes a rotary pump having an inner section in which vanes slide radially within slots in a rotor, engaging an inner surface of a casing ring having an inner diameter greater than the outer diameter of the rotor. The rotor and casing ring turn together, but the center of rotation of the casing ring is displaced from that of the rotor, so that fluid working spaces, bounded by adjacent vanes, by the outer surface of the rotor, and by the inner surface of the casing ring, are formed to vary in volume with the rotation of the rotor. The casing ring also includes a number of shafts, extending axially in each direction into circumferential slots in pistons mounted to slide radially within the rotor, so that these pistons are driven in a reciprocating motion by the eccentricity of the casing ring with the rotation of the rotor, forming additional fluid working chambers inside and outside the pistons. When the device is operated as a pump, fluid is brought through a hollow portion of the rotor shaft, into the chambers associated with the central inner section, through internal slots into other working chambers, and outward through a second hollow portion of the rotor shaft.